Linz is the third-largest city of Austria and capital of the state of Upper Austria (German: Oberösterreich). It is located in the north centre of Austria, approximately 30 km south of the Czech border, on both sides of the river Danube. The population of the city is 189,284 (2009), and that of the Greater Linz conurbation is 271,000. The main street "Landstraße" leads from the "Blumauerplatz" to the main square. In the middle of this square the high "Pestsäule" ("plague column", also known as "Dreifaltigkeitssäule" (Dreifaltigkeit means Holy Trinity)) was built to remember the people who died in the plague epidemics.Near the castle, being the former seat of Friedrich the III — the oldest Austrian church is located: Sankt/Saint Martins church. It was built during early medieval Carolingian times.